Method for preventing crystal formation in a dispersion of a liquid in a matrix

ABSTRACT

An improved method for the manufacture of transdermal drug delivery devices comprising liquid dispersions of a liquid in an aqueous or nonaqueous matrix is disclosed. More particularly, the invention relates to preventing the formation of a crystalline structure in such liquid dispersions by annealing films and laminates in-line immediately following film formation and/or lamination during the manufacture of these devices.

This application is a continuation of U.S. application Ser. No.09/144,718, filed Sep. 1, 1998, now abandoned, which is a continuationof U.S. application Ser. No. 08/951,943, filed Oct. 17, 1997 now U.S.Pat. No. 6,569,448, which is a continuation of U.S. application Ser. No.08/566,228, filed Dec. 1, 1995, abandoned.

FIELD OF THE INVENTION

This invention relates to the manufacture of dispersions of a liquid inan aqueous or non-aqueous matrix and to drug delivery devices whichutilize these liquid dispersions. More particularly, the inventionrelates to preventing the formation and/or growth of a crystallinestructure in films or laminates comprising such liquid dispersions byannealing the films and/or laminates immediately following filmformation and/or lamination. The crystal-free films and laminates maythen be formed into various articles, such as drug delivery devices.

BACKGROUND OF THE INVENTION

As used herein, “annealing” refers to a process of subjecting the liquiddispersion or article formed therefrom to a specified, elevatedtemperature for a predetermined minimum period of time and then allowingthe dispersion or article to cool to ambient conditions.

Transdermal delivery devices comprising a dispersion of a drug or otherbiological agent in various aqueous or non-aqueous matrices are known inthe art as described in U.S. Pat. Nos. 3,598,122, 3,598,123, 4,031,894,4,144,317, 4,201,211, 4,262,003, 4,379,454, and 4,436,741, all of whichare incorporated herein in their entirety by reference. As disclosed inthese patents, aqueous matrices typically comprise water orwater/ethanol and 1–5 wt. % of a gelling agent such ashydroxyethylcellulose. Non-aqueous matrices are typically comprised of apolymeric material such as copolymers of ethylene vinyl acetate orblends of low molecular weight and high molecular weight polyisobutene.The drug may be in solid form or in the form of a liquid dispersion.This invention relates to such liquid drug dispersions.

In addition to the above mentioned patents, U.S. Pat. No. 5,370,924,incorporated herein in its entirety by reference, discloses methods formanufacturing transdermal drug delivery devices. The methods disclosedin this patent describe a process whereby the various elements of atransdermal device may be fabricated separately and joined together in afinal manufacturing step.

Although this invention will be described hereafter specifically withrespect to scopolamine delivery devices, it should be recognized that itis applicable to dispersions of any other drug or biological agent inmatrices where a crystalline structure may be formed. Such drugs oragents such as nicotine, secoverine, and benztropine, for example, may,to the extent they form crystalline structures, be treated in a mannersimilar to the methods by which dispersions of scopolamine base aretreated according to this invention.

Transdermal delivery devices for the administration of scopolamine ofthe type disclosed in U.S. Pat. No. 4,031,894 cited above are usedextensively for the prevention of motion sickness. The originalmanufacture of the product is described in the patent by solvent castingof chloroform solutions of scopolamine base in polyisobutene (PIB) andmineral oil (MO) onto impermeable webs to form drug reservoir andcontact adhesive films. Upon evaporation of the chloroform, a dispersionof liquid scopolamine base in the PIBIMO matrix is formed. The drugreservoir and contact adhesive films are then laminated to oppositesides of a release rate controlling membrane, formed from a mineral oilimpregnated microporous film, to produce a final laminate comprising aremovable release liner layer, an adhesive layer, a rate controllingmembrane layer, a drug reservoir layer, and an impermeable backinglamina. The final laminate is then die cut into individual systems andpackaged in individual heat sealed pouches.

The manufacture of the product in this manner was carried out forapproximately five years without any indication of the formation ofcrystals in either the drug reservoir or the adhesive. After that time,small crystals of scopolamine hydrate were observed infrequently butthis did not present a problem because the release rate of the drug fromthe device was not affected by the presence of the small number of smallcrystals then occurring. In addition to the small number and size of thecrystals, another reason that the release rates were not affected isattributed to the observation that the crystal size did not changeappreciably (i.e. minimal if any crystal growth) with time in the pouch.

Approximately two years later, larger numbers of rapidly propagatingcrystals were observed in the drug reservoir, with a lower incidenceobserved in the contact adhesive layer which contained a lowerconcentration of scopolamine base. At that time, the size of thecrystals and their frequency of occurrence had increased to the pointwhere they produced a significant adverse effect on the release rate ofscopolamine from the device. Thereafter, every lot manufactureddeveloped unacceptably high crystal size and frequency and commercialproduction had to be halted until the problem could be solved.

Crystallization was most noticeable after the step in which the finallaminate film was cut into individual devices. After the final laminatefilm was fed through the die-cutting machine for the formation ofindividual transdermal delivery units, crystallization began around theedges of the cut product and crystalline growth thereafter propagatedrapidly throughout the mass of the reservoir and in some cases theadhesive layer. Visually observable crystals were not necessarilyapparent immediately after the cutting step; instead they wouldtypically develop over a period of days. These crystals were identifiedas a hydrate form of scopolamine base.

Various attempts to eliminate the problem were tried over the nextseveral months, all to no avail. For example, the drug reservoir film,adhesive film, and the final laminate film were heated overnight, yetcrystallization after die-cutting still occurred. Similarly, the castingsolutions were heated and allowed to stand for extended periods alsowith no effect. Attempts to reduce the amount of residual water in thechloroform solution of the scopolamine base by drying with extra amountsof drying agents such as anhydrous sodium sulfate and magnesium sulfatewere also unsuccessful as crystallization still occurred. Extensivecleaning of contacting surfaces reduced but did not eliminate thepresence of crystals after die-cutting.

A successful process for the prevention of the formation of thescopolamine hydrate crystals was ultimately discovered and is describedin U.S. Pat. No. 4,832,953, incorporated in its entirety herein byreference. According to that invention, formation of crystallinehydrates in a liquid dispersion of a hydratable liquid in a non-aqueous,typically polymeric, matrix can be prevented if, after they have beenplaced in their packages, the articles are heated to a temperature abovethe melting point of the crystalline hydrate, are maintained at thattemperature for a period of time, and then are allowed to cool toambient conditions. For this process to be successful, holding times forcast films and laminates, prior to die-cutting, pouching, and annealing,were minimized in an effort to outrace the kinetics of crystal growth.It was found that when so treated, crystals initially presentdisappeared, did not reform upon cooling to ambient conditions, andthere were no additional signs of crystal formation or growth afterstorage at ambient conditions and under accelerated aging conditions forseveral months.

The commercial manufacture of the product including the step ofannealing the pouched systems as described in U.S. Pat. No. 4,832,953was then-carried out for approximately seven years before the currentcrystallization problem developed and commercial production again had tobe halted. The measures employed to prevent formation of the hydrate astaught in the U.S. Pat. No. 4,832,953 are not effective in preventingthe formation of the newly observed crystals because: 1) the newcrystals do not melt at the annealing temperatures specified therein;and 2) the kinetics of the new crystal growth are significantly faster,such that films cannot practically be moved through the manufacturingprocess fast enough to eliminate significant crystal growth. Crystalshave been observed only four hours after film casting and have beenobserved in the final product.

An extensive investigation was undertaken, including examination of rawmaterials, process equipment, and procedures to isolate a source ofcrystallization, during which it was determined that crystal formationcould not be attributed to any specific feature of the procedures,equipment, or raw materials used to produce the product. It wasconfirmed that rapid crystallization could start after any manufacturingstep involving the scopolamine films and laminates. Production washalted until the problem was solved according to this invention.

SUMMARY OF THE INVENTION

The new crystal has been identified as a crystalline form of anhydrousscopolamine base. The cause of the change from the previous hydrate formto a more stable anhydrous crystal form is unknown. The inventors havefound that the annealing of all the individual scopolamine-containingfilms and laminates, in addition to the final laminate and pouchedsystem, successfully prevents the formation and growth of the currentlyobserved scopolamine crystalline structure. The invention provides amethod to effectively beat the crystal growth kinetics in a practicalmanner.

It is accordingly an aspect of this invention to prevent the formationand/or growth of a crystalline structure in a dispersion of a liquid inan aqueous or non-aqueous matrix.

It is another aspect of this invention to prevent the formation and/orgrowth of a crystalline structure of scopolamine in dispersions ofscopolamine base in a non-aqueous matrix.

It is another aspect of this invention to manufacture transdermaltherapeutic systems for the controlled delivery of scopolamine basewhich are free from crystals of scopolamine.

It is yet another aspect of this invention to provide an improved methodof manufacture of transdermal therapeutic systems which prevents theformation and/or growth of a crystalline structure in dispersions of aliquid in an aqueous or nonaqueous matrix.

These and other aspects of this invention will be readily apparent fromthe following description of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow diagram depicting the process of forming the drugreservoir/backing layer according to a preferred embodiment of thisinvention.

FIG. 2 is a flow diagram depicting the process of forming the ratecontrol membrane/contact adhesive layer according to a preferredembodiment of this invention.

FIG. 3 is a flow diagram depicting the process of forming the finallaminate according to a preferred embodiment of this invention.

FIG. 4 is an isometric view of an in-line annealing oven useful for thepurposes of the present invention.

DISCLOSURE OF THE INVENTION

According to this invention, formation and/or growth of a crystallinestructure in a dispersion of a liquid in an aqueous or non-aqueousmatrix can be prevented if, immediately following the formation of eachand every film or laminate of the dispersion, the layer(s) containingthe liquid dispersion is (are) sandwiched between non-porous films andsubjected to an annealing process wherein they are heated to asufficient temperature for a sufficient time and then allowed to cool.Preferably, the following conditions are satisfied at each annealingstep: 1) the melting point temperature of the crystal is exceeded; 2)sufficient time is provided to allow the crystal to melt; 3) thedispersion is protected from environmental exposure until the nextmanufacturing (and annealing) step; and 4) the annealing step beginspromptly after film formation and/or lamination. Films and laminatestreated by this annealing process are stable and have been observed toremain crystal-free after storage at ambient conditions for at least 90days.

A preferred embodiment of this invention is directed to the manufactureof transdermal delivery devices. It has been found that transdermaldelivery devices manufactured according to this invention are free fromcrystals and exhibit release rates within applicable specifications forthe product. Although this invention will be described with respect to aspecific example relating to the manufacture of transdermal deliverydevices for the controlled delivery of scopolamine, it should berecognized that this invention is applicable to the processing ofdispersions of any liquid agent capable of forming a crystallinestructure.

According to this preferred embodiment, individual films and laminatesof a transdermal therapeutic system which comprise a dispersion of aliquid in a matrix, as well as the final laminate and pouched system,are subjected to an annealing process immediately following theformation of the films or laminates. The annealing process is performedimmediately after the film is placed between two non-porous substratesin order to minimize exposure of the film to the atmosphere. The film orlaminate thus treated is stable with respect to crystal growth until thenext processing step, assuming exposure of the annealed film to theenvironment is controlled.

In a particularly preferred embodiment directed to the manufacture oftransdermal delivery devices containing scopolamine, the rate controlmembrane/contact adhesive films, drug reservoir films, and finallaminate films are protected between two non-porous substrates and aresubjected to an annealing process, immediately following lamination, andare heated to a sufficient temperature, for a sufficient time, and thenallowed to cool to ambient conditions in order to prevent subsequentcrystal formation and growth. The final laminate is then cut intoindividual systems, placed into sealed containers, and then subjected toan additional annealing step.

The formation of the films and laminates may be achieved by any meansknown in the art. Although this invention will be described with respectto an example wherein a solvent casting procedure is utilized to formthe various films, it should be recognized that other procedures forforming the films, such as extrusion or reverse roll coating, may beused in the practice of this invention. For example, if an extrusionprocess is used to form the various films, it would not be necessary touse the drying ovens in the manufacturing processing line and theextruded films would proceed directly to the annealing oven or to alamination stage immediately followed by the annealing step of thisinvention.

The annealing of the films and laminates can be achieved by variousmeans. For example, when the films are formed by solvent casting,annealing can be performed by a second pass through the drying ovensthat are used to dry the initial film. This requires that by the timethe last portion of film has exited the ovens for the first time theportion of film that first exited the ovens has not already begun tocrystallize. Alteratively, the film casting may be broken up into smallsublots so that any film or laminate is subjected to annealing within afew hours of casting or lamination. Preferably, annealing occursin-line, immediately following film formation and/or lamination. Mostpreferably, an annealing oven is placed immediately after the laminationstage.

The manufacture of transdermal delivery devices using a solvent castingprocedure will now be described with reference to the drawings. Theprocess for the formation of the drug reservoir layer is shown inFIG. 1. The drug reservoir casting solution is cast onto impermeablebacking layer 21 fed from source roll 11 to form a film comprising drugreservoir layer 22 on impermeable backing layer 21. The film is thenpassed through the drying ovens 20 to evaporate the solvent. The driedfilm is then passed through a laminator 30 where non-porous interleavinglayer 32 is applied to the surface of drug reservoir layer 22. Thelaminate is then passed through in-line annealing oven 40, shown indetail in FIG. 4. After exiting the annealing oven, the laminate iswound up on take-up roll 31 of the laminator.

The rate control membrane/contact adhesive layer is formed by a similarprocess as shown in FIG. 2. The contact adhesive solution 51 is castonto release liner 50 and passed through the drying ovens 20. Ratecontrol membrane 52 and non-porous interleaving layer 53 are thenlaminated to the surfaces of the contact adhesive and rate controlmembrane, respectively. The laminate is then passed through the in-lineannealing oven 40 before being taken up on the take-up roll 31 of thelaminator.

The final laminate is produced as shown in FIG. 3. The drug reservoirlaminate and rate control membrane/contact adhesive laminate rolls areset up in the laminator. Interleaving layer 53 is removed from the ratecontrol membrane/contact adhesive laminate and interleaving layer 32 isremoved from the drug reservoir laminate, exposing the rate controlmembrane 52 and drug reservoir 22, respectively, which are thenlaminated together to form the final laminate. The final laminate,comprising impermeable release liner 50, contact adhesive layer 51, ratecontrol membrane 52, drug reservoir layer 22, and impermeable backinglayer 21, is then passed through in-line annealing oven 40 before beingtaken up once again on take-up roll 31 of the laminator. In a finalprocessing step (not shown), individual systems are die cut from thefinal laminate. The systems are placed in individual pouches, thepouches are heat sealed and the pouched systems are then placed in anin-line annealing oven for a final annealing process.

FIG. 4 depicts annealing oven 40 in greater detail. The laminate firstenters the annealing oven where it contacts heated roll 41 whichprovides immediate heating to the laminate. The laminate passes overidler rolls 42 and tension roll 43 and is passed through the annealingchamber 44 which is preheated to a predetermined temperature. Thedwelling time of the laminate in the annealing chamber may be adjustedby setting an appropriate line speed for the laminate. Annealing oven 40is also provided with air handler 45 and access door 46.

As seen in the above description, at each film forming/laminating step,the adhesive is sandwiched between non-porous substrates so that afterannealing is performed, additional contamination by crystal seeds is notpossible until the next processing operation. After each intermediatefilm or laminate is annealed, that product is stable until the nextoperation, as long as it is not exposed to the atmosphere.

The use of an in-line annealing oven offers several advantages toalternative methods of annealing individual films and laminates. First,it eliminates the need for breaking the production down into smallsublots in order to reduce film exposure time, thus allowing forproduction at the previous full lot capacity. Such a method also reducesthe film exposure time more effectively to only a matter of seconds.Additionally, the use of an in-line annealing oven allows for betterutilization of the casting ovens and avoids the difficulty in handlingthe laminates as would be required if they were to be run through thecasting ovens a second time. With the in-line annealing method of thisinvention, better prevention of crystal formation is observed becauseonly seconds elapse between the time that the film leaves the castingovens and enters the annealing oven, effectively beating crystal growthkinetics by eliminating any time available for crystal formation and/orgrowth.

The temperature and time are not critical provided they are adequate toprevent the formation of crystals after cooling and are not so high asto cause damage to the individual films or laminas. If crystals areinitially present, the temperature must be at, and preferably above, themelting point of the crystal and the time should be sufficient to causemelting of all the crystals present. If crystals are not present at thetime of the heating step, temperatures lower than the melting point ofthe crystal may be effective. Nevertheless, it is preferable from thepoint of quality assurance and uniformity of processing conditions toheat above the melting point of the crystal, the formation of which itis desired to prevent.

In the preferred embodiment of this invention directed to the preventionof the formation of scopolamine crystals during the manufacture oftransdermal therapeutic systems containing scopolamine, the temperatureto which the individual and final laminates were heated is preferablywithin the range of 75–90° C., for a duration of 2–10 minutes. The finalpouched systems are preferably heated to a temperature of 75° C. for aperiod of 4–24 hours. The actual temperature for other materials iseasily determined by measuring the melting point of the crystal.

Having thus generally described our invention, the following specificexample is provided to illustrate the invention. The example is notintended to limit the scope of the invention in any way. Unlessotherwise indicated, parts are by weight.

EXAMPLE 1

Preparation of Scopolamine Base Solution

Scopolamine base was formed by dissolving scopolamine hydrobromide in anaqueous sodium bicarbonate-sodium carbonate buffer solution. Sodiumhydroxide was added until a pH of about 9.6 was reached at which pointthe scopolamine base precipitated from solution and was extracted withchloroform.

Preparation of Casting Solutions

20.0 parts high molecular weight PIB (Vistanex L-100, 1,200,000viscosity average molecular weight), 26.1 parts low molecular weight PIB(Vistanex LM-MS, 35,000 viscosity average molecular weight), 41.7 partsmineral oil (10 cp at 25° C.) and 11.3 parts of scopolamine base weredissolved in chloroform in a mixer to prepare the drug reservoir castingsolution used in forming the drug reservoir film.

To prepare the contact adhesive casting solution, a solution of 23.1parts of said high molecular weight PIB, 28.8 parts of said lowmolecular weight PIB, 46.1 parts of said mineral oil, and 2.0 parts ofsaid scopolamine base were dissolved in chloroform in a mixer.

Preparation of Films and Laminates

The drug reservoir casting solution was then solvent cast to form a drugreservoir film approximately 50 micrometers dry thickness on anapproximately 65 micrometer backing of aluminized polyethyleneterephthalate (Scotchpak®). The drug reservoir film was passed throughan oven to evaporate the chloroform, leaving behind a drug containingadhesive film on a backing substrate. After leaving the oven, the filmwas moved to a laminator where an interleaving film was applied. Thelaminate was then passed into a second oven placed immediately followingthe laminator, where the laminate was heated to a temperature of 80–85°C. for 9–10 minutes. Thereafter, the laminate is returned to the take-uproll on the laminator.

The rate control membrane/contact adhesive laminate was similarlyprepared by solvent casting a 50 micrometer dry thickness adhesive layerof the contact adhesive casting solution onto a 75 micrometersiliconized, polyethylene terephthalate film. After casting, the filmswere passed through the ovens to evaporate the chloroform solvent,leaving behind a drug containing adhesive on a release liner. This filmwas moved to a laminator, where a microporous polypropylene ratecontrolling membrane, with the pores saturated with mineral oil, waslaminated to the adhesive surface. An interleaving film was added toprotect the top of the control membrane and the entire laminate wasintroduced into the second oven immediately thereafter and was heated toa temperature of 80–85° C. for 5–6 minutes.

The rate control membrane surface of the rate control membrane/contactadhesive laminate was then laminated to the drug reservoir surface ofthe drug reservoir laminate to yield a final laminate. This finallaminate was then also passed through the annealing oven immediatelyfollowing the laminator and heated to a temperature of 80–85° C. forapproximately 2 minutes. 2.5 cm² circular disk-shaped systems werepunch-cut from the resulting five layer laminate. The individual systemswere then packaged within heat-sealed foil-lined pouches. The poucheswere then treated by heating in an additional annealing oven to 75° C.for 4–24 hours and thereafter allowed to cool to ambient conditions.

None of the systems made according to the invention were observed tocontain crystals. Additionally, systems made according to the inventionexhibited release rates within the applicable specifications for theproduct.

Having thus described our invention, it is readily apparent that variousmodifications can be made by workers skilled in the art withoutdeparting from the scope of this invention. It is intended that theinvention embrace these equivalents within the scope of the claims thatfollow.

1. A process for the production of a scopolamine free base containingtransdermal system substantially free of crystals of scopolamine freebase, comprising annealing scopolamine free base containing layers ofsaid transdermal system at a temperature above the melting point of thecrystals for a period of time sufficient to melt scopolamine free baseanhydrous crystals, wherein the annealing process is performed aftercasting a scopolamine free base containing formulation onto a web orafter forming a laminate with a scopolamine free base containingformulation for use in constructing said transdermal systemsubstantially free of scopolamine free base anhydrous crystals.
 2. Theprocess of claim 1, wherein said transdermal system is further packagedand further heat treated at a temperature of at least 67° C. to about90° C. for a period of about 4 hours to about 24 hours.
 3. The processof claim 1 wherein said annealing takes place at about 75° C. to about90° C.
 4. The process of claim 1, wherein said annealing takes placeover a period of about 2–10 minutes.
 5. The process of claim 1, whereina drug reservoir layer containing scopolamine free base and a contractadhesive layer containing scopolamine free base are each separatelyannealed, then contacted and further annealed prior to packaging.
 6. Amethod for manufacturing delivery devices for the transdermaladministration of scopolamine comprising, in combination: a. forming alaminate, at lease one lamina of which comprises a dispersion of saidscopolamine in a non-aqueous matrix; b. cutting subunits forming saiddelivery devices from said laminate; c. packaging said delivery devicesin sealed containers; d. heating said delivery devices in saidcontainers to a temperature above the melting point of anhydrouscrystalline scopolamine and maintaining said delivery devices at suchtemperature for a time sufficient to prevent the formation or eliminatethe presence of anhydrous crystals of scopolamine for a substantialperiod of time after cooling of the subunits to ambient temperatures;and e. cooling the delivery devices to ambient temperatures; wherein theheating comprising heating at least each scopolamine containing layer toa temperature exceeding the melting point of scopolamine anhydrouscrystal for a period of time sufficient to melt the crystals, theheating step being conducted prior to or during the process, oflaminating and/or sealing the scopolamine containing layer.
 7. A processfor the production of a scopolamine free base containing transdermalsystem substantially free of anhydrous crystals of scopolamine freebase, comprising annealing scopolamine free base containing layers ofsaid transdermal system at a temperature above the melting point of theanhydrous crystals for a period of time sufficient to melt the crystals,wherein the annealing process is performed within a period after castinga scopolamine free base containing formulation onto a web for use inconstructing said transdermal system so as to result in a transdermalsystem substantially free of anhydrous scopolamine crystals, whereinsaid annealing takes place at about 75° C. to about 90° C.
 8. Theprocess of claim 1, wherein the heating and annealing process is doneimmediately after casting a scopolamine free base containing formulationonto a web or immediately after forming a laminate with a scopolaminefree base containing formulation.
 9. The process of claim 1, furthercomprising annealing the transdermal system at a temperature above themelting point of scopolamine after packaging in pouch.
 10. The processof claim 1, further comprising annealing a laminate that includes ascopolamine free base containing layer laminated to a nonporousnon-scopolamine-containing layer.
 11. The process of claim 10, furthercomprising removing the nonporous non-scopolamine-containing layerbefore packaging the transdermal system in pouch.
 12. The process ofclaim 1, comprising two heating and annealing steps, one heating stepbeing immediately after casting the scopolamine free base containingformulation onto a web.